Britian's 'flash' purchasing managers' index survey fell more than expected to 51.7 this month, S&P Global said on Thursday.
Expectations had been for a drop to 52.5, against September's 52.6, with declines in both the service and manufacturing sectors bringing the figure down.
Services PMI fell to 51.8 from 52.4, while the manufacturing PMI dropped to 50.3 from 51.5, with both expected to remain unchanged from September's reading.
S&P Global said the October data "pointed to a moderate increase in UK private sector output, but the rate of expansion slowed for the second month running to its lowest since November 2023".
Respondents to the PMI survey commented on the impact of delayed decision making among clients and heightened economic uncertainty in October, with next week's Budget likely to be a big reason.
Employment was a particularly weak spot, with overall staffing numbers decreasing for the first time in 2024, the report said.
EY ITEM Club analysts noted another cut to base interest by the Bank of England in next month’s meeting was all but set in stone after the figures.
Declines within both the services and manufacturing sectors supported the view that "the Bank of England will likely continue cutting rates at a relatively gradual pace”, analysts said, adding a 25-basis-point cut was a “near certainty”.